This invention relates to semiconductor processing, and more particularly to an improved apparatus for cleaning semiconductor wafers.
Wafer cleaning is an essential process in the manufacture of semiconductor devices. A number of other processes (notably chemical-mechanical polishing or CMP) leave residues on the wafer surface; such residues must be removed as completely as possible before further processing can be performed.
Two broad categories of wafer cleaning apparatus may be characterized as xe2x80x9croller-typexe2x80x9d and xe2x80x9cpencil-type.xe2x80x9d A typical roller-type wafer cleaning apparatus (shown, for example, in U.S. Pat. Nos. 5,937,469 and 5,976,267) includes a roller with a brush parallel to the wafer surface and extending across the wafer; the roller turns on its axis while the wafer rotates underneath it. A pencil-type cleaning apparatus, on the other hand, has a cleaning head mounted on a shaft which is perpendicular to the wafer surface and can move radially across the surface.
A typical pencil-type wafer cleaner is shown schematically in FIG. 1. The wafer 1, only the outer portion of which is shown, is mounted in a wafer chuck 2. The wafer chuck is generally connected to a shaft (not shown) for spinning the wafer at high speed, in order to facilitate rapid and thorough drying of the wafer. While the details of the wafer chuck design vary between cleaning tools, it should be noted that there is in general a portion 2a of the wafer chuck above the plane of the wafer surface being cleaned.
The pencil-type wafer cleaner 10 includes a cleaning head 11 connected to a shaft 12. The portion 11a of the cleaning head in contact with the wafer is approximately hemispherical in shape. This portion, at least, has a brush, sponge or the like for removing foreign material from the wafer surface. Shaft 12 is connected to a mechanism (not shown) which moves the wafer cleaner 10 in the radial direction. The wafer is thus efficiently cleaned as the cleaning head moves radially across the surface of the spinning wafer.
However, as shown in FIG. 1, the arrangement of head 11 and wafer chuck 2 can prevent the complete cleaning of the wafer. Mechanical interference between the cleaning head 11 and the wafer chuck 2 (at contact point 2c shown in FIG. 1) results in the point of cleaning contact 11p lying some radial distance inward from the edge of the wafer. An annular uncleaned region 1e thus remains near the edge of the wafer. This problem is commonly termed xe2x80x9cedge exclusion.xe2x80x9d
It is possible to rotate the wafer by using rollers engaging the edge of the wafer; these rollers leave most of the area exposed, so that the cleaning head 11 may move unimpeded to the wafer edge (see U.S. Pat. No. 5,937,469 and Japanese patent publication JP 11-97397). However, such wafer edge rollers generally cannot spin the wafer at a high speed as is required for fast drying.
There remains a need for a pencil-type wafer cleaner which permits center-to-edge and edge-to-edge cleaning without edge exclusion, and which is compatible with a variety of wafer chuck arrangements.
The present invention addresses the above-described need by providing an apparatus for cleaning a surface of a wafer without edge exclusion. The apparatus includes a wafer holding mechanism with a portion contacting the outer edge of the wafer and having a surface substantially planar with the wafer surface. The apparatus further includes a wafer cleaning head including a wafer cleaning element; the wafer cleaning element has a flat surface contacting the wafer surface when cleaning the wafer. A portion of the wafer cleaning element overlies the above-mentioned surface of the wafer holding mechanism when cleaning the edge portion of the wafer. The wafer holding mechanism and wafer cleaning head are shaped to avoid mechanical interference therebetween when the edge portion of the wafer is cleaned.
The wafer cleaning element may be a brush, a sponge, or other suitable material.
As part of a pencil-type wafer cleaner, the apparatus also includes a shaft connected to the wafer cleaning head, the axis of the shaft being substantially perpendicular to the wafer surface.